So, what is the point of buying a better specced and more expensive player, if one does not get better performance?
I wish there was a site that meausured these things objectively, so that we could see or not differences between players. Secrets of home theater and hifi had a great measuring routine back in the early days of DVD players. They would produce objective numbers and tests on DVD players. It would be nice to have something like that these days.
I think you are looking at the problem through old analog equipment eyes.
In the days of disc and magnetic tape superb procesion engineering was key to excellent results. In the digital era the same rules and considerations do not apply.
Things changed with the advent of the CD. In fact the price pyramid inverted in many ways. So the players that cost the most, had the most trouble playing discs. The founder of Hyperion audio, Ted Perry, actually said that the probability of a player able to play most discs was INVERSELY related to price. This was brought home to me, when I had to do a minor repair on a friends MacIntosh disc player. I found that the disc drive was the cheapest of cheapest Sanyo drive!
So a player need an accurate laser tracking system and the ability to send an error free digital stream. Generally, the AVR, AVP or TV does the decoding. Generally there is not really significant audible differences between DACs. The processors do vary though, and will be in the receiving device as a rule.
Now picture quality can vary, but again this will be largely determined by the receiving device. I noted a better picture with my AV 10, and also the processing and sound field was improved, especially for high quality Atmos streams.
So for disc players it really comes down to the ability to track most dics, and provide a stable digital stream. Quite a bit of this is totally independent on the cost of the device. The only other consideration is that if it built like a "tank" it might have a longer life, but again no guarantees.
So, my advice stands, that the only thing you will gain by adding another player is a back up device. You will not get anything else.